TOPIC: rectifier test

how would i go about testing a rectifier in a 1969 65hp.
thanks in advance.

Easiest is to test the stator.

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What ohms do you read yellow to yellow. And one yellow to ground.

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If battery does not charge then it either the stator or rectifier.

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If stator is good , then rectifier is bad

to test put omh meter on the battery terminal and one yellow terminal then reverse them one way will have continuity and reversed will have none then test the other yellow terminal the same way with the same results.only 2 diodes to check.

Here are the directions for testing the Merc rectifier:
(Disconnect all leads first)

Rectifier Test sequence for ‘60s ‘70s ‘80s Mercury O/B

Terminals A & C are different than Terminal B.
Terminal B is the (+) terminal. (you will find a tiny + symbol near it)

Dis-connect all leads & use R x 1000 on your meter.
With the red lead plugged into the (+) port on your meter and the black lead plugged into the (-) port on your meter:

Red lead to ground (rectifier metal case or powerhead) and black lead to A = continuity
Red lead to ground and black lead to C = continuity
Black lead to ground and red lead to A = NO continuity
Black lead to ground and red lead to C = NO continuity
Black lead to B and red to A = continuity
Black lead to B and red to C = continuity
Red lead to B and Black lead to A = NO continuity
Red lead to B and Black lead to C = NO continuity

Tah-Dah

I have also attached a scan of how to test the Mercury stator that only has (2) yellow leads.

thanks i was able to find a good one in my "junkyard". a friend of a friend had trouble starting his engine that had been running last week. when i went over to look the new battery he installed had the cables reversed and the switchbox and rectifier got fried.

Dr. Frankenmerc Help .. I think I have it right ,just want to make sure Do you have a photo of the rectifier wiring .. something doesn't look right on my 70 ,70 hp engine ?? Still having problems,won't turn over, I even replaced the neutral safety switch with a new one.. and the old one was still good !. I jumped the neutral safety switch and it still wouldn't turn over, Jumped the starter solenoid and it turns over ??? I checked every wire on the engine and control box..I give up ??

just wondering, when you turn the key to the start position are you getting 12 volts across the two small posts on the solenoid?

@65G3,

If you are still looking at the rectifier as the no crank problem you are barking up the wrong tree. A bad rectifier will not prevent the issue you are experiencing. I am attaching a wiring diagram that while not specific to your 70 hp the starting systems are essentially identical. If you intend to perform your own repairs I would suggest the purchase of a DVM,and at the very least a simple test light. The DVM will also allow you to test continuity of circuits as well as voltage are relatively inexpensive at Radio Shack and this week Harbor Freight had them on sale for $3.00. You probably spent more for the neutral safety switch.

You need power at the terminal with the yellow wire at the solenoid when the key is turned to the start position and the other terminal with black wire needs to be grounded. If you have no power to that yellow wire you need to start back tracking towards the ignition switch and that is where using a DVM for continuity test comes in handy by first checking at the main plug connections in between engine harness and control harness.If you have power at this terminal and good ground I'd suspect a bad solenoid.
Melanie



FGI:(For General Information) I am a former shop manager and ASE master tech, built,wired,etc countless street rods,hot rods,show cars ,you name it 30+ trs.

Ok ..Thanks I'm going to check the ignition switch. That's the only thing I overlooked, It "Was" working, I heard they sometimes get corrosion inside the contacts , Now looking for my multimeter

I would not jump straight to the ignition switch. Test for power at the yellow wired terminal when keyed to start and test for a good ground at the black wired terminal. If you do have power there you have pretty much isolated it to a bad solenoid. No power when keyed to start then I would check for battery voltage at the red wire at the ignition switch. No power there check harness to engine plug. I would also check for a fuse as I believe in your original post you only momentarily shorted the positive and negative cables.

I was having intermittent no start with my 1984 115hp Merc so I wired in a HD push button back by the transom in a protected spot by running a 14 gauge wire from the yellow terminal on the solenoid and another 10 gauge wire direct to the battery. This worked out great but it by-passes the neutral safety switch.Then while checking things under the cowling I notice that a fuse didn't really fit one end of the fuse holder very tightly. Just a little tweak to tighten and my no start problem was solved or at least it hasn't presented itself again.

Oh Man ..I gotta thank you !!! You guys are great !!! I've been knocking myself out checking this , checking that . I took apart the control unit at least a dozen times !!! Check wires ,neutral safety switches, I had my test meter on today .. and guess what ?? It was the freaken plug on the side of the motor !!! , I cleaned the little connections with fine fine emory cloth .. cleaned inside the female end of the plug . connected the battery ..and she turned over.. then I tried it again.. and it wouldn't turn over!! Agghhh . Well at least I isolated the problem .. Now I'm gonna see if I can get a tighter connection on the plug !!

Way to go!!! That's great and thanks for posting your results.

Melanie

Turns out the male contacts were all loose inside the rubber plug itself ,corrosion set in breaking the wires off , I'm going to have to get either a new plug or try slitting the plug open with a razor to see if I can re solder them , if a plug is available I can splice the cables together, I really don't want to replace the whole complete cable,cause then I have to take the control box apart again,then the ignition switch apart, and the choke switch

Here's the plug and contacts

if that is the connector then you have a 3 cyl 65 not a 4cyl 1969 65.

It's a 1970 70 HP 3 cylinder

I don't know know whats going on with this board I only posted 1 time , I came back and I see 4 posts ????

If you are unable to find a replacement plug and have some excess cable coming from the controls you could install a terminal strip somewhere convenient or better yet I like to use this type of connectors that can be picked up at most any automotive parts house......

cgi.ebay.com/ebaymotors/Sea-Doo-XP-GSX-GTX-SPX-SP-SPI-GS-Electrical-Connectors-/110708410173?pt=Personal_Watercraft_Parts&hash=item19c6bc473d

While not completely watertight they do have silicone seal that does a fair job.That's the green part you see and each individual wire socket also has the same seal. I use them as quick disconnects on items such as VHF radio,depth/fish finder,or where most would use a butt connector.

I'd retain the stock plug and pass the individual wires through it and neatly seal them with with silicone after snipping off the wires and male connectors. Good luck and good job hanging in there.
Melanie

I sliced the back of the plug,opened it up and " Sure Enough"
there it was in plain view the yellow and gray wire ...were corroded off from corrosion !! I took the pins out de -soldered the little holes . had to add new wires inside the plug. Now I'll seal the heck out of it ..and put the plug in !!! All this testing switches,starter, solenoid,ground wires ,controls took so much time, and the problem was in the plug !Well it lasted 41 years !!!

Glad you got it all sorted out, and it didn't cost an arm and a leg to fix! Great reference material provided by "the gang" for future use too, IMO. Thanks everybody!

Well I fixed the problem , replaced the 2 wires inside the plug, (Yellow & Grey) .. siliconed the plug back together and "Walla" It Starts

Congratulations!!! Time to reward yourself and go cruzin.

Melanie